1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method that form an image while conveying a long band-like sheet-like recording medium.
2. Description of the Related Art
In recent years, in order to accommodate the demand to diversify and increase the volume of information processing, printers serving as image forming apparatus have been used which enable high-speed processing by adopting an electrophotographic image-making process and using continuous paper (continuous sheet paper) as the recording medium (transfer medium).
Among such high-speed printers, there is a printer that uses, as the recording medium, continuous paper in which feed holes (called “pin holes” below) are formed at equidistant intervals continuously in the feeding direction in both edge portions of the paper. The printer is disposed with a tractor including pins that fit into the pin holes in the continuous paper, and is configured to convey the continuous paper by rotating the tractor. The continuous paper is retained as a result of the pins of the tractor fitting into the pin holes, whereby the continuous paper is prevented from becoming slack on the conveyance path.
The portions at both edges of the continuous paper and in which the pin holes are formed at equidistant intervals are used simply for the tractor of the printer to convey the continuous paper. Thus, both edge portions become unnecessary after the continuous paper has been printed, and are cut off and discarded in a later processing step. Consequently, the demand is rising for an image forming apparatus that can convey, as the recording medium, painless continuous paper, in which pin holes are not disposed, in order to prevent both edge portions of the continuous paper from becoming useless and to cut back on the processing cost for cutting off both edges of the continuous paper.
Also, in view of the characteristics of the conveyance motor that is driven in order to convey the paper, a certain amount of time is needed in such high-speed printers in order to bring the conveyance motor up to a constant speed when printing is started, or to stop the conveyance motor from the constant speed when printing is stopped. Consequently, it is common for such high-speed printers to conduct control to bring the conveyance motor up to a constant speed while the continuous paper is conveyed a certain length X and, when printing is stopped, to stop the conveyance motor at the point in time when the continuous paper has been conveyed a certain length Y.
Here, it is desirable for such high-speed printers to be capable of continuous printing to ensure that when the printer conducts intermittent printing or resumes printing after printing has been stopped, the continuous paper is conveyed in the opposite direction by an amount corresponding to the length of X+Y when printing is stopped so that there is no useless white paper (blank spaces) of the lengths X+Y arising due to positional displacement of the continuous paper, so that it is difficult for useless white paper to arise.
Thus, image forming apparatus in the related art which can convey painless continuous paper as the recording medium are configured so that continuous paper having no pin holes is supplied from a paper supply section and nipped by a drive roller pair. The drive roller pair is rotated while nipping the continuous paper, whereby the continuous paper is frictionally conveyed counter to the braking force of a tension imparting component for taking up the slack. An oblique roller, which is disposed in a paper position regulating section disposed on the conveyance path and is arranged obliquely with respect to an axis orthogonal to the paper conveyance direction, rolling contacts the paper, whereby one side edge of the continuous paper is made to glidingly contact an edge guide, without imparting the braking force, and the continuous paper is positioned. Then, the continuous paper is conveyed into a printing section disposed on the conveyance path between the oblique roller and the drive roller pair, and printing is conducted.
Moreover, image forming apparatus in the related art which can convey painless continuous paper as the recording medium include a buffer roller disposed between the printing section and the oblique roller of the paper position regulating section. The buffer roller is driven by a drive component such as a motor to contact the surface of, and absorb the slack in, the continuous paper in accordance with a back feed amount where the drive roller pair for frictional conveyance is reversely rotated to convey the continuous paper in the opposite direction when printing is stopped.
The buffer roller configures a buffer component that is driven by the drive component so as to separate from the surface of the continuous paper while the continuous paper is being printed by the printing section. When printing is stopped or started, the buffer component is driven by the drive component to contact, push, and separate the surface of the continuous paper from the linear conveyance path at the time of printing, to ensure that the recording paper does not become slack (e.g., see Japanese Patent Application Publication (JP-A) No. 2004-155533).
Image forming apparatus in the related art which can convey painless continuous paper as the recording medium have the problem that they include plural mechanisms because the recording paper buffer component is disposed between the oblique roller and the printing section. Also, because the buffer component is disposed between the oblique roller and the printing unit, there are problems in that there are variations in the position of the recording paper that is positioned as a result of the oblique roller causing the recording paper to glidingly contact the edge guide, the behavior of the paper at the time printing starts becomes unstable, and the printing precision at the start of printing deteriorates in comparison to when printing is conducted on paper including pin holes (sprocket-fed paper).